1. Field of the Invention
This invention relates, generally, to systems for storing and delivering fibrous material to concrete mixers. More particularly, it relates to systems for storing and delivering fibrous material to concrete mixers which uniformly meter the fibers prior to distribution to the concrete mixers.
2. Description of Prior Art
Synthetic fibrous material or fibers, based on polypropylene, polyester, or nylon, are often added to concrete mixes primarily to improve resistance to cracking, but with other benefits such as enhanced impact resistance, toughness, and impermeability. In fact, the desirability of employing fibrous reinforcing material in concrete has been known for a number of years. The use of synthetic fibers does not replace the traditional steel reinforcement rods but acts as a secondary reinforcement to enhance the properties and integrity of the concrete matrix.
Generally, synthetic fibers are available in two physical forms: monofilament fibers with a round cross section having a diameter of 20 to 50 microns and lengths of one-quarter inch (1/4") to one inch (1"), and fibrillated fibers produced by slitting drawn or stretched polymer films and re-interconnected forming a net-like array. The fibrillated fibers are used typically in small bundles and can be one-half inch (1/2") to two and one-half inches (21/2") long with the cross section of each individual fiber being rectangular having dimensions of approximately 40 microns by approximately 300 microns.
In most situations, the fibers are added to the concrete in an amount ranging from one-half pound (1/2 lb.) to three pounds (3 lb.) or more per cubic yard, depending on the application. For convenience, the fibers are packed in preweighed bags of one-half pound (1/2 lb.) to ten pounds (10 lb.) or more, which can be added directly into a ready-mixed concrete truck. originally, the bags of fibers were made of plastic which were opened, emptied into the truck, and then discarded. More recently, the fibers have been packaged into paper bags that can be put directly into the concrete mixer. The type of paper used for the bags depends on its ease of degradability in the concrete mix.
There are several disadvantages in adding the preweighed bags, either plastic or paper, of fibers to the ready-mixed concrete trucks. First, the preweighed bags have a low bulk density which equates directly to high freight and storage costs. Second, the actual process of filling the bags is time consuming and costly. Third, the actual cost of the bag itself is significant and provides no useful purpose in the concrete. Fourth, manual placement of the bags into the ready-mixed concrete trucks adds additional time to the process, impedes the flow of traffic at the concrete mixing plant, and increases safety risks for concrete plant employees.
Most recently, automated fiber dispensing systems have been developed in attempts to overcome these disadvantages. For example, automated dispensing systems have been the subject of several patents including U.S. Pat. Nos. 5,529,247 and 5,407,139 to Mleczewski, U.S. Pat. No. 3,618,684 to Burke et al., U.S. Pat. No. 3,099,368 to Turner et al., U.S. Pat. No. 4,591,021 to Moran et al., to name a few.
However, each of these systems has shortcomings. For example, some of these systems are not easily controlled to dispense a given weight of fibers. In addition, these systems do not provide for a means for the steady continuous removal of bulk fibers for addition into the concrete mixer as the stone, sand, cement, and water are added to give complete and automated dispersion of the fibers.
Another shortcoming is the inability to limit or control the amount of fibers released to the atmosphere at the end of the dispensing delivery system. Typically, a truck can often be 100 to 150 feet from the dispenser system, and the dispensing delivery means to the truck can often be 20 feet above the inlet to the cement truck mixer. Considerable volumes of air are required to insure the fibers are reliably transported through the tube; a side effect of this is that some fibers are blown back into the atmosphere. This reduces the accuracy of the dispensing system and is environmentally unfriendly and unacceptable.
In view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the needed automated fiber dispensing system could be provided.